This invention relates to an optoelectronic monitoring device that has at least one light source and at least one receiving element in accordance with the preamble of claim 1 and a testing method therefor in accordance with the preamble of claim 16.
Optoelectronic monitoring devices are used for a multitude of tasks ranging from preventing thefts to securing dangerous machines which must be timely automatically deactivated when an object and particularly when operating personnel approaches it. Technically particularly challenging are monitoring devices capable of measuring distances which not only detect the presence of an object but which also determine the distance to where it is located.
Such a distance determination is especially useful in connection with movable robots that pass an area that is used by operators and other personnel. For example, the robot might generate a warning beginning at a certain distance, or it can change to a slower operating mode, and when the robot passes a critical distance, it can be stopped altogether. Movable robots which are continuously subjected to changing scenes that come into their fields of view present particularly difficult problems.
For automobiles, cameras are used which take distance-resolved pictures in real time to optimize the controls for airbags, for example. In the case of an approaching accident, the release of the airbags can be adjusted depending on the sitting positions of the occupants that is determined on the basis of their distances. In addition, distance resolving pictures are used to recognize and classify other traffic, such as cars, bicycles or pedestrians. A further use is to automatically maintain distances from vehicles that are in front.
A requirement for monitoring is that the sensors which take a picture of the monitored region function properly. For example, they must be able to distinguish if the actual pictorial or video information corresponds to the external conditions, or if the picture has been “burned in”. This is not easily determined because a constant picture might be caused by scenery that does not change or by a malfunction of the sensor.
WO01/78411 discloses a test method for picture sensors which are capable of processing brightness information for testing the functionality of the pixels. For this, a fixed contrast pattern of a monitored region can be moved relative to the picture sensor, the brightness of even individual zones or areas can be changed with additional illumination or with a movable test object, or a testing pattern can be used to check the functionality of the sensor. These approaches are not useful for determining distances when they involve variations in the brightness. Further, movements, whether by the sensor or separate testing objects, require mechanical structures and must vary not only the brightness, but also the distances.
It is further known to use laser scanners in which a laser beam is scanned over a monitored region, for example with a rotating mirror, and the respective distances are determined on the basis of the reflected light. A reference target can be positioned in a portion of the sector through which the laser beam is scanned, and it can even be positioned inside the housing for the monitoring device. The device is functional if it correctly determines the distance to the reference target. However, this approach also requires movable parts for scanning the laser beam. Further, if receiving chips are used which generate a linear or two-dimensional matrix-like distance picture instead of a laser beam, this testing method cannot be used.
German patent publication DE 101 38 960 A1 discloses an apparatus for monitoring a space with two picture-taking units that are arranged at a 90° angle with respect to each other. The two picture-taking units take pictures of the entire space, and distances are calculated on the basis of differences in the brightness at the two picture-taking units. The functionality of the units is checked with a self-test by turning the illumination of the space on and off to thereby render the observed scene dynamic. This is sufficient to check whether the device reacts at all, but involves no checking if the distances calculated from the brightness differences are in fact correct.
German patent publication DE 10 2004 035 243 A1 teaches a camera arrangement for monitoring a dangerous area by temporally changing its illumination, for example by modulation, and the resulting changes are detected by a test sensor. The device then tests its functionality by checking whether the pictures taken by the camera vary appropriately from a change determined by the test sensor. This does not involve checking the measured distances, because the camera arrangement cannot per se determine distances since it operates two-dimensionally.